1. Field of the Invention
The present invention relates to a positioning device and a group of accessories for use in conjunction with a spectrometer. More particularly, the invention is used in conjunction with a Fourier Transform IR Spectrometer (FTIR) and possesses an X-Y-Z translation state with the added capability of an angular adjustment in the X-Y plane, which enables the use of a large group of precisely geometrically tailored accessories. The accessories are mounted on the translation stage and enable the spectroscopist to obtain IR spectra of liquid, solid and gas samples as desired.
2. Description of Prior Art
IR analysis requires that a liquid, solid or gas sample be placed in a suitable sampling device, known as an IR accessory, and positioned in a beam of IR light in the sample compartment of an IR spectrometer.
Prior to 1980, IR spectrometers required minutes to obtain a spectrum and the energy in the instrument was low. As a result, a number of accessories were developed for enhancing the IR energy incident upon the sample by using a small auxiliary optical bench with a multiplicity of mirrors and lenses. One device in wide use, termed a beam condenser, focused the energy beam in the IR spectrometer to a small diameter in order to determine spectra of samples as small as a few square millimeters.
A second type of accessory device in wide use from the early 1960's is ATR (Attenuated Total Reflectance) in which a solid sample such as plastic or fiber or a liquid sample is placed in optical contact with a flat optical plate of well defined geometry. Sting, U.S. Pat. No. 5,015,092 (assigned to Spectra-Tech, Inc.) summarizes the present state of the art. A series of books by James A. Harrick explores fully the multiplicity of these devices. In all cases it is essential that four or more mirrors are required to precisely focus light on the sample being investigated. The ATR accessories are difficult to focus, are expensive and require that the device be geometrically matched to the particular IR spectrometer being used, of which there are several manufacturers and many types. The ATR crystals necessary have been summarized by Wilks, a pioneer in the field, in 1980 and consist of a flat plate with parallel sides, trapezoidal or parallelogram in cross section, and cylindrical elements.
With regard to precise sample positioning in the IR spectrometer sample beam, a single X-Y-Z positioning device was developed for microsampling with an FTIR instrument. Spec Ac, in the early 1980's briefly marketed a small X-Y-Z sampling stage capable of accommodating a micro sample of solid, liquid or gas. The device was particularly tailored to one type of IR spectrometer, and had no provision for blocking stray radiation from reaching the detector of the IR instrument. It is essential that all radiation which reaches the detector of the IR instrument has transited the attenuated total reflectance crystal. Stray radiation vitiates all the quantitative features of an IR spectrum. There was no provision for angular adjustment.